17/2/2014 Electrode - Wikipedia, the free encyclopedia

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Electrodes used in arc welding

ElectrodeFrom Wikipedia, the free encyclopedia

An electrode is an electrical conductor used to makecontact with a nonmetallic part of a circuit (e.g. asemiconductor, an electrolyte or a vacuum). The wordwas coined by the scientist Michael Faraday from theGreek words elektron (meaning amber, from which the

word electricity is derived) and hodos, a way.[1]

Contents

1 Anode and cathode in electrochemical cells

1.1 Primary cell

1.2 Secondary cell2 Other anodes and cathodes

3 Welding electrodes4 Alternating current electrodes

5 Uses

6 Chemically modified electrodes7 See also

8 References

Anode and cathode in electrochemical cells

An electrode in an electrochemical cell is referred to as either an anode or a cathode (words that were alsocoined by Faraday). The anode is now defined as the electrode at which electrons leave the cell and oxidationoccurs, and the cathode as the electrode at which electrons enter the cell and reduction occurs. Each electrodemay become either the anode or the cathode depending on the direction of current through the cell. A bipolarelectrode is an electrode that functions as the anode of one cell and the cathode of another cell.

Primary cell

A primary cell is a special type of electrochemical cell in which the reaction cannot be reversed, and theidentities of the anode and cathode are therefore fixed. The anode is always the negative electrode. The cell canbe discharged but not recharged.

Secondary cell

A secondary cell, for example a rechargeable battery, is one in which the chemical reactions are reversible.When the cell is being charged, the anode becomes the positive (+) and the cathode the negative (−) electrode.This is also the case in an electrolytic cell. When the cell is being discharged, it behaves like a primary cell, withthe anode as the negative and the cathode as the positive electrode.

Other anodes and cathodes

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In a vacuum tube or a semiconductor having polarity (diodes, electrolytic capacitors) the anode is the positive(+) electrode and the cathode the negative (−). The electrons enter the device through the cathode and exit thedevice through the anode. Many devices have other electrodes to control operation, e.g., base, gate, controlgrid.

In a three-electrode cell, a counter electrode, also called an auxiliary electrode, is used only to make aconnection to the electrolyte so that a current can be applied to the working electrode. The counter electrode isusually made of an inert material, such as a noble metal or graphite, to keep it from dissolving.

Welding electrodes

In arc welding an electrode is used to conduct current through a workpiece to fuse two pieces together.Depending upon the process, the electrode is either consumable, in the case of gas metal arc welding or shieldedmetal arc welding, or non-consumable, such as in gas tungsten arc welding. For a direct current system the weldrod or stick may be a cathode for a filling type weld or an anode for other welding processes. For an alternatingcurrent arc welder the welding electrode would not be considered an anode or cathode.

Alternating current electrodes

For electrical systems which use alternating current the electrodes are the connections from the circuitry to theobject to be acted upon by the electric current but are not designated anode or cathode since the direction offlow of the electrons changes periodically, usually many times per second.

Uses

Electrodes are used to provide current through nonmetal objects to alter them in numerous ways and to measureconductivity for numerous purposes. Examples include:

Electrodes for fuel cellsElectrodes for medical purposes, such as EEG, ECG, ECT, defibrillator

Electrodes for electrophysiology techniques in biomedical researchElectrodes for execution by the electric chairElectrodes for electroplating

Electrodes for arc weldingElectrodes for cathodic protection

Electrodes for groundingElectrodes for chemical analysis using electrochemical methods

Inert electrodes for electrolysis (made of platinum)Membrane electrode assembly

Chemically modified electrodes

Chemically modified electrodes are electrodes that have their surfaces chemically modified to change theelectrode's physical, chemical, electrochemical, optical, electrical, and transport properties. These electrodes are

used for advanced purposes in research and investigation.[2]

See also

17/2/2014 Electrode - Wikipedia, the free encyclopedia

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Working electrodeReference electrode

BatteryRedox Reaction

Cathodic protectionGalvanic cell

Anion vs. CationElectron versus hole

ElectrolyteElectron microscope

NorylTafel equationHot cathode

Cold cathodeElectrolysis

References

1. ^ Faraday, Michael (1834). "On Electrical Decomposition" (http://www.webcitation.org/5mq8a85S3).Philosophical Transactions of the Royal Society. Archived from the original (http://chimie.scola.ac-paris.fr/sitedechimie/hist_chi/text_origin/faraday/Faraday-electrochem.htm) on 2010-01-17. Retrieved 2010-01-17. ( (in which Faraday coins the words electrode, anode, cathode, anion, cation, electrolyte, electrolyze)

2. ^ Durst, R., Baumner, A., Murray, R., Buck, R., & Andrieux, C., "Chemically modified electrodes:Recommended terminology and definitions (PDF)(http://old.iupac.org/publications/pac/1997/pdf/6906x1317.pdf)", IUPAC, 1997, pp 1317–1323.

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